documentation comment

src/tile.rs

@@ -5,7 +5,9 @@ use crate::image::animation_frames_from_string;
 pub struct Tile {
     pub id: String,
     pub name: Option<String>,
-    pub wall: Option<bool>, // this is "optional" in that a tile can have `WAL true|false` or neither
+    /// this is "optional" in that a tile can have `WAL true`, `WAL false` or neither
+    /// obviously Some(false) is the same as None but we want to preserve the original formatting
+    pub wall: Option<bool>,
     pub animation_frames: Vec<Image>,
     pub colour_id: Option<u64>,
 }